1. Field of the Invention
The present invention relates to a case for accommodating a solid-state imaging device, and a solid-state imaging apparatus comprising the same.
2. Related Background Art
Though hollow cases made of ceramics have conventionally been used for solid-state imaging apparatus for a long time, hollow cases made of resins have recently been under development in order to cut their material cost down.
In the ceramic cases, the thermal expansion of the ceramics is on a par with that of lead frames or solid-state imaging device made of a metal or the like and that of a transparent plate or the like made of glass or the like. Therefore, deformations such as distortion and warping by heating and the like at the time of forming the case or mounting the solid-state imaging device are so small that they are not problematic in particular. In a case made of a resin, however, the difference in thermal expansion between the resin and a metal, glass, or the like is so large that the case is usually deformed greatly by heat at the time of molding or mounting. Such a deformation may shift the focal point of incident light, which is problematic in that the solid-state imaging device fails to read images accurately and so forth.
For example, a hollow case made of a resin in which the volume ratio between a case part located higher than a lead frame and a case part located lower than the lead frame is set in order to prevent the case from deforming at the time of mounting has been proposed (see Patent Document 1). The document proposes to suppress the warping at the time of integral molding by setting the volume ratio between the upper and lower parts of the case such that the case upper part volume/case lower part volume=1:1.6 to 1:1.8.
In cases formed from a resin by injection molding and the like, however, the resin is likely to have an anisotropy in coefficient of thermal expansion, whereby the coefficient of thermal expansion may differ between the bottom plate and side wall part of the case depending on how the resin flows into the case at the time of molding, which causes the warping when heating/cooling the case. Therefore, the warping of the case is hard to suppress by simply regulating the volume ratio between the upper and lower parts of the case as in Patent Document 1 (Japanese Patent Application Laid-Open No. HEI 11-330285), thus making it necessary to regulate dimensions of the bottom plate and side wall part of the case in order to control how the resin flows into the case at the time of molding.